In the production of cardboard sheets, for example the manufacture of boxes from an endless web of cardboard, it is frequently necessary to change the arrangement of the lengthwise creasing and cutting lines in accordance with the orders being processed. In general, the orders relate to rather limited quantities, so that in this field of the art the speed and punctuality of the alteration of the position of the folding and cutting tools becomes extremely important. To this end, machines of various types have been devised, initially with manual operation--that is to say with manual positioning and changing of the tools--and currently with automatic or semi-automatic operation. Among the most advanced machines for the creasing and cutting of endless webs of cardboard, of a known type, are machines which possess at least two pairs of creasing rollers, that is to say rollers bearing the creasing tools, and at least two pairs of cutting rollers. During operation, a single pair of creasing rollers and a single pair of cutting rollers are active; the second pair of creasing rollers and the second pair of cutting rollers are inactive and are arranged in an attitude which permits the moving and the positioning of the tools fitted thereon. A pair of robots provides for the displacement of the cutting and creasing tools on the pair of cutting and creasing rollers which are presently inactive, according to a program which depends on the next order which is to be processed. When the tools on the inactive rollers have been positioned and the processing of the previous order is completed, the attitude of the machine is modified in order to exchange the positions of the pairs of rollers, that is, to bring the rollers which were previously inactive into the working position, and deactivate those which were previously active, thus permitting the robots to position the creasing and cutting tools for a later order.
The known machines of this type possess a number of disadvantages. In many of said machines, in fact, the plane in which the web of cardboard runs has to be modified when the attitude of the machine is adjusted, that is to say when a pair of cutting rollers and a pair of creasing rollers are deactivated while another pair of cutting rollers and another pair of creasing rollers are activated. This entails risks of irregular operation, and additionally makes it necessary to use mobile surfaces for the running of the cardboard, which surfaces have to change attitude at each transition from the processing of one order to the processing of a subsequent order. In addition to the high cost and a particular complexity of control, these machines are also very bulky, in that the mobile running surfaces project substantially, upstream and downstream of the cutting and creasing zone. This is particularly disadvantageous not only because it entails an increase in the overall length of the processing line, but also because it impedes the insertion of these automatic machines into prearranged processing lines which are currently equipped with machines having manual tool replacement. These machines being of much more limited size.
Furthermore, this arrangement of the pairs of cutting and creasing rollers in the machines of the known type renders the latter particularly bulky. In fact, in many of these machines the first pair of creasing rollers and the first pair of cutting rollers are arranged upstream (relative to the direction of movement of the cardboard web) of the second pair of creasing rollers and the second pair of cutting rollers. This entails a further increase in the lengthwise bulk of the machine.
A further problem associated with this type of processing lies in the need to exchange the tools as rapidly as possible in order to increase the productivity of the plant.